Process for impregnating porous bodies with a solid fusible substance



Sept. 12, 1967 T. P. GALLAGHER 3,341,355 PROCESS FOR IMPREGNATING POROUS BODIES WITH A SOLID FUSIBLE SUBSTANCE Filed Oct. l9, 1962 IN VENTOR. 7i/0MAs P 61411461452 Al's ATTORNEYS United States Patent 3,341,355 PROCESS FOR IMPREGNATING POROUS BODIES WITH A SOLID FUSIBLE SUBSTANCE Thomas P. Gallagher, Orange, Conn., assignor to The Fuller Merriam Company, West Haven, Conn., a corporation of Connecticut Filed Oct. 19, 1962, Ser. No. 231,644 4 Claims. (Cl. 117-113) The invention relates to a process for impregnating porous bodies with'a solid fusible substance. It is especially intended to secure a more uniform impregnation of the porous body than heretofore possible with previously known methods.

The usual procedure for impregnating a porous body with a fusible substance is to heat the impregnating substance until it becomes a liquid and then immerse the body therein. As the body heats up the liquid flows into the pores of the body until all of the pores are filled. At this point, if the body is removed from the liquid, the liquid will tend to run out body will c-ool inwardly from the outside, a skin will form at the outer edge portions of the body while the still molten liquid on the inside will drain toward the bottom of the body and solidify there.

Another method of impregnating a porous body is to place the body within an enclosed tank. Air is then removed from the tank to create a vacuum. Thereafter the fusible substance in liquid form is pumped into the tank whereit enters the body. After a suitable soak period, the excess liquid is pumped out of the tank and the body is removed.

The same drawbacks mentioned above with respect to the first method are also present in this second method. Due to the fluid state of the fusible substance within the pores of the body at the time the tank is pumped out, the liquid therein tends to either flow out of the body or to drain toward the bottom thereof.

Various mechanical expedients have been tried to overcome these drawbacks and to secure uniform impregnation of the body. These expedients have included rotating the body about its own axis or turning the body repeatedly end over end or from side to side, all in an attempt to keep the fusible substance uniformly distributed throughout the porous body as the substance cools to a solid state. The results of these attempts have been negative; a nonuniform filling of the pores is still obtained.

Still another method has been employed for impregnating porous bodies and while this method does avoid the drawbacks of the above-mentioned methods, it is, nevertheless, accompanied by other disadvantages. In this third method the porous body is immersed in the molten liquid with which it is desired to impregnate the body, After a soak period sufficiently long to permit all of the pores in the body to be filled, the molten liquid with the body still in it is allowed to cool down and to solidify. When the liquid is entirely solidified, the body immersed therein is chipped out. While this method does secure uniform impregnation of the body with the fusible substance it is, of course, subject to the necessity for chipping the body out of the hardened fusible substance and to the resultant delays and increased labor costs attendant thereto.

The present invention has for its object the development of an improved method for impregnating porous bodies with a solid fusible substance that will the disadvantages of the prior known methods described above. More specifically, it is the object of the present invention to develop an impregnating method that will uniformly fill the pores of the bodies in such a manner that little or no manual labor will be required so that the method will readily lend itself to automation.

of the body. Also, since the These objectives are realized by the inventive process which, briefly and in general, comprises immersing one or more porous bodies in a molten bath of the fusible substance with which it is desired to impregnate the bodies. The body of the bath is continuously heated so as to maintain the liquid molten for a soaking period during which the liquid fusible substance flows uniformly into all of the pores of the bodies being done. After the soaking period, the bodies are then Withdrawn from the molten liquid very, very slowly. During the withdrawal of the bodies from the molten liquid the heating of the liquid bath is controlled so as to maintain the upper surface of the liquid at a temperature as close to the temperature of fusion as is possible without actually reaching the solidifying temperature. When the temperature of the surface of the liquid is stabilized just above the fusion point of the substance, the bodies are raised from the liquid. The exit speed at which the bodies are withdrawn is purposely kept extremely low so that as the pieces break the surface of the molten liquid, the liquid within the pores passes from its liquid state to a solid state before it can be displaced from the pores.

In essence the inventive process contemplates the regulation of the temperature gradient in the heating vessel such that the fusion temperature for the liquid impregnat ing substance exists closely adjacent the surface of the liquid and the concomitant regulation of the exit speed of the bodies being impregnated such that the fusion temperature is reached at tially as soon as those liquid bath.

By this means the impregnating liquid in the pores of the bodies can be solidified in place before the liquid has an opportunity to drain to other pores in the bodies at a lower 'level. A uniform deposition of the impregnating substance throughout the porous body is thereby achieved without the necessity for solidifying the bath and chipping out the bodies.

One of the many applications for the process of the invention is in the impregnation of grinding wheels and segments. For the purpose of illustrating one way in which the invention may be practiced the invention will presently be described in detail with reference to this particular application. However, it will be clear to those in the art that the invention is not limited to this specific use but may be applied to other porous objects as well. The description to follow and the accompanying drawings are, therefore, by way of example only and are not intended to define or restrict the scope of the invention. The claims appended hereto, together with their lawful equivalents, are relied upon for that purpose.

Of the drawings:

FIG. 1 is a side elevation view, in section, of apparatus for carrying out the process of the invention, showing a grinding wheel immersed in a molten liquid bath within a heating vessel; and

FIG. 2 is an enlarged sectional view through the grinding wheel as it slowly emerges from the molten liquid.

Referring now to the drawings, and at first to FIG. 1, there is shown a vessel 10 that is provided with a series of electrical heating coils 12, 12 around the inner side 12, 12 melts and maintains a molten bath of sulphur 14. Immersed within the molten sulphur 14 is a porous body or work piece which, in this instance, comprises a grinding wheel 16. The grinding wheel 16 is supported on a basket 18 that is suspended by a frame 20 from any suitable device (not shown) for raising and lowering the basket into and out of the molten sulphur.

Sulphur has a fusion point of 239 input to the sulphur bath 14 from the 12 is suflicient to keep the sulphur above various points in the body substanpoints rise above the level of the F. and the heat heating coils 12, this temperature 3 in a molten state after the grinding wheel has been lowered into the bath. The grinding wheel 16 is retained within the molten sulphur bath 14 for a soaking period during which time a thermal equilibrium is established between the wheel 16 and the liquid sulphur 14 and the pores of the wheel fill up with liquid.

At this point, if it has not been done earlier, the heat input to the coils 12, 12 is so regulated as to stabilize the temperature of the surface of the molten sulphur just above the fusion point. This may be done, for example, by placing a bimetallic thermostat 22 on the side of the vessel just above the liquid level and connecting the thermostat into a control circuit (not shown) for the heating coils 12, 12.

The basket 18 is then raised out of the molten bath of sulphur 14 at a very slow exit speed so that as each new section of the grinding wheel 16 rises above the liquid level of the sulphur 14, the liquid sulphur trapped in the pores of the wheel solidifies before it can drain from the pores to a lower level in the wheel. This is illustrated in FIG. 2 in which the grinding wheel 16 is shown partially out of the liquid sulphur 14. In the upper portion 24 of the wheel 16, that is, the portion of the wheel extending above the liquid level of the sulphur, the liquid sulphur trapped in the pores of this section has solidified while the liquid sulphur in the pores of the portion 26 of the wheel 16 below the level of the bath is still in a molten state. The rate of the exit speed of the basket 18 and the grindingwheel 16 is maintained below the rate at which the sulphur solidifies within the pores of the wheel as the wheel emerges above the liquid level of the impregnating bath.

One example in which the process has been used successfully is in the impregnation of sulphur in grinding segments. Segments measuring 11 inches by 6 inches by 2 inches have been uniformly impregnated with sulphur by this method employing exit speeds of between to inch per hour.

An additional advantage of the process of the invention is that the density of the deposit of the impregnating substance can be varied without impairing the uniformity of the deposit. In the example just given it was found that the density of the sulphur was decreased at the higher exit speeds yet the uniformity of the sulphur deposit was not impaired.

It will be apparent that the process of the invention is not limited to any specific impregnating substance. Any substance that has a fusion temperature above room temperature may be utilized. The invention may be used to impregnate grinding wheels and other porous bodies with other suitable substances as, for example, with paraffin or rosin. Another substance that may be used, particularly for grinding wheels, is naphthalene. By varying the exit speeds of the bodies and by maintaining the surface temperature of the impregnating substance just above the fusion temperature uniform impregnation of a porous body with most fusible substances can be obtained,

What is claimed is:

1. A process for the impregnation of a porous body with a solid fusible substance, said process comprising,

heating the impregnating substance above its melting temperature to form a bath of molten liquid, immersing the porous body in the molten bath and retaining the body therein until all of the pores of the body are filled with the liquid of the bath, maintaining the surface of the liquid bath at a temperature just above the fusion temperature of the impregnating substance, and continuously withdrawing the porous body through the surface of the liquid bath at a low incremental rate that is not in excess of the rate of solidification of the liquid impregnating substance trapped within the emerging increment of the body immediately above the surface of the liquid bath. 2. A process for the impregnation of a porous body with a solid fusible substance, said process comprising,

heating the impregnating substance above its melting temperature to form a bath of molten liquid,

immersing the porous body in the molten bath and retaining the body therein until all of the pores of the body are filled with the liquid of the bath,

maintaining the surface of the liquid bath at a temperature just above the fusion temperature of the impregnating substance, and

continuously withdrawing the porous body through the surface of the liquid bath at a low incremental exit speed at which the liquid trapped in the pores of the emerging increment of the body reaches the temperature of fusion substantially as soon as such increment emerges above the liquid level of the bath.

3. A process for the impregnation of a porous body as set out in claim 2 wherein the porous body is a grinding wheel and the fusible substance is sulphur.

4. A process for the impregnation of a porous body with a solid fusible substance, as defined in claim 2, which further includes the step of sensing the ambient temperature adjacent the surface of the liquid bath and utilizing the temperature sensed to control the heating of the molten liquid bath to maintain the surface of the bath at a temperature just above the fusion temperature of the impregnating substance.

References Cited UNITED STATES PATENTS 1,615,271 1/1927 Hartmann 51-307 1,900,430 3/1933 Daniels 117113 X 2,267,597 12/1941 Neville et al 117113 X 2,333,480 11/1943 Jackson 5l295 ALFRED L. LEAVITT, Primary Examiner.

RICHARD D. NEVIUS, Examiner. 

1. A PROCESS FOR THE IMPREGNATION OF A POROUS BODY WITH A SOLID FUSIBLE SUBSTANCE, SAID PROCESS COMPRISING, HEATING THE IMPREGNATING SUBSTANCE ABOVE ITS MELTING TEMPERATURE TO FORM A BATH OF MOLTEN LIQUID, IMMERSING THE POROUS BODY IN THE MOLTEN BATH AND RETAINING THE BODY THEREIN UNTIL ALL OF THE PORES OF THE BODY ARE FILLED WITH THE LIQUID OF THE BATH, MAINTAINING THE SURFACE OF THE LIQUID BATH AT A TEMPERATURE JUST ABOVE THE FUSION TEMPERATURE OF THE IMPREGNATING SUBSTANCE, AND CONTINUOUSLY WITHDRAWING THE POROUS BODY THROUGH THE SURFACE OF THE LIQUID BATH AT A LOW INCREMENTAL RATE THAT IS NOT IN EXCESS OF THE RATE OE SOLIDIFICATION OF THE LIQUID IMPREGNATING SUBSTANCE TRAPPED WITHIN THE EMERGING INCREMENT OF THE BODY IMMEDIATELY ABOVE THE SURFACE OF THE LIQUID BATH. 